Without limiting the scope of the present invention, its background will be described in relation to actuating hydraulically operated well testing tools, as an example.
In oil and gas wells, it is common to conduct well testing and stimulation operations to determine production potential and enhance that potential. For example, hydraulically operated downhole tools have been developed which operate responsive to pressure differentials in the wellbore that can sample formation fluids for testing or circulate fluids therethrough. These tools typically incorporate both a ball valve and lateral circulation ports. Both the ball valve and circulation ports are operable between open and closed positions. Commonly, these tools are capable of operating in different modes such as a drill pipe tester valve, a circulation valve and a formation tester valve, as well as providing its operator with the ability to displace fluids in the pipe string above the tool with nitrogen or another gas prior to testing or retesting. A popular method of employing the circulating valve is to dispose it within a wellbore and maintain it in a well test position during flow periods with the ball valve open and the circulation ports closed. At the conclusion of the flow periods, the tool is moved to a circulating position with the ports open and the ball valve closed.
To actuate such hydraulically actuated well tools, a hydraulic control system is typically use. In certain installations, the hydraulic control system has been positioned at the surface. It has been found, however, that it is uneconomical to run the required hydraulic control lines from the surface to the hydraulically actuated well tools for well testing. Accordingly, attempts have been made to position the hydraulic control system downhole. These downhole hydraulic control systems have typically used control valves having sliding sleeves, poppets and the like that include o-rings or other elastomeric seals to selectively control fluid communication. It has been found, however, that due to large pressure differentials, limitations on size, temperature extremes and near zero leak rate tolerance, conventional hydraulic control valves that utilize elastomeric seals are not suitable.
Therefore, a need has arisen for an improved hydraulic control system for actuating downhole tools. In addition, a need has arisen for such an improved hydraulic control system that does not require hydraulic control lines running from the surface to the hydraulically actuated well tools. Further, a need has arisen for such an improved hydraulic control system that does not utilize control valves having elastomeric seals to selectively control fluid communication.